does good service with them: for he is the great water scavenger.
Decaying vegetable matter is his food, and with those jaws he will
bark a dead stick as neatly as you will with a penknife. But he does
not refuse animal matter. A dead brother (his, not yours) makes a
savoury meal for him; and a party of those Vorticellae would stand a
poor chance if he came across them. You may count these caddis baits
by hundreds of thousands; whether the trout eat them case and all, is
a question in these streams. In some rivers the trout do so; and
what is curious, during the spring, have a regular gizzard, a
temporary thickening of the coats of the stomach, to enable them to
grind the pebbly cases of the caddises. See! here is one whose house
is closed at both ends--'grille,' as Pictet calls it, in his
unrivalled monograph of the Genevese Phryganeae, on which he spent
four years of untiring labour. The grub has stopped the mouth of his
case by an open network of silk, defended by small pebbles, through
which the water may pass freely, while he changes into his nymph
state. Open the case; you find within not a grub, but a strange
bird-beaked creature, with long legs and horns laid flat by its
sides, and miniature wings on its back. Observe that the sides of
the tail, and one pair of legs, are fringed with dark hairs. After a
fortnight's rest in this prison this 'nymph' will gnaw her way out
and swim through the water on her back, by means of that fringed tail
and paddles, till she reaches the bank and the upper air. There,
under the genial light of day, her skin will burst, and a four-winged
fly emerge, to buzz over the water as a fawn-coloured Caperer--
deadliest of trout flies; if she be not snapped up beforehand under
water by some spotted monarch in search of supper.

But look again among this tangled mass of weed. Here are more larvae
of water-flies. Some have the sides fringed with what look like